The present invention relates to a lower structure of an automotive vehicle which comprises a pair of side frames which extends forwardly from a front portion of a vehicle room and a suspension cross member provided behind or below a power unit which is arranged between the pair of side frames and extends in a vehicle width direction.
Many structures which can absorb the vehicle-collision energy properly so as to restrain the collision load from having bad influence on passengers in a vehicle room in the vehicle frontal collision or the like, by using retreat of a power unit arranged at a vehicle front portion, have been proposed.
Generally, a suspension cross member supporting a suspension arm for a front vehicle is provided behind or below the power unit. Accordingly, a retreat of the power unit may be hindered by the suspension cross member.
For this reason, according to conventional structures, the suspension cross member is forcibly detached from a vehicle body by breaking (tearing) rubber bushes provided attachment portions of the suspension cross member to the vehicle body in the vehicle frontal collision.
However, since some kinds of vehicles have no rubber bush at the attachment portions, but both plate-shaped members having a high (great) rigidity are fastened directly by bolts, the suspension cross member could not be detached easily from the vehicle body.
Accordingly, many structures which can easily detach the suspension cross member from the vehicle body in order to provide the smooth retreat of the power unit in the vehicle frontal collision have been conventionally proposed.
For example, Japanese Patent Laid-Open Publication No. 6-329045 discloses a structure in which a bracket connected to a side frame on the side of the vehicle body is provided separately from a suspension cross member body, and this bracket is detached from the suspension cross member body in the vehicle frontal collision, so that the suspension cross member can be detached from the vehicle body
Japanese Patent Laid-Open Publication No. 2002-2528 discloses a structure in which a notch opening upwardly is provided at an arm portion of a suspension cross member (chassis cross member), and a control ring with a slit opening vertically is provided. In this structure, when a drive shaft hits against the arm portion so that a specified load acts on this arm portion in the vehicle frontal collision, the slit of the control ring easily causes deformation and breakage of the control ring. Consequently, the arm portion gets separated off bolts, so that the suspension cross member can be detached from the vehicle body.
Japanese Patent Laid-Open Publication No. 2004-148960 discloses a structure in which the suspension cross member and the side frame on the side of the vehicle body are fastened with bolts via a connecting arm extending vertically, and a slit is formed at an upper end portion of the connecting arm. Accordingly, the suspension cross member can be detached easily from the front frame in the vehicle frontal collision.
However, in case the structure is constituted so that the suspension cross member can be detached easily from the vehicle body like the above-described conventional structures, there is a problem in that the support rigidity, in the vehicle width direction, of the suspension cross member during the normal vehicle traveling would be decreased.
For example, according to the structure disclosed in the above-described first patent document, the support rigidity, in the vehicle width direction, of the suspension cross member is not considered at all. Therefore, the above-described easy detachment of the suspension cross member from the bracket would improperly decrease the support rigidity, in the vehicle width direction, of the suspension cross member during the normal vehicle traveling.
According to the structures disclosed in the above-described second or third patent documents, meanwhile, the rigidity of the connection portion of the arm portion to the vehicle body (side frame) is decreased uniformly in the vehicle direction by the slit formed at the arm portion. Thereby, the conventional structures of the second and third patent documents would improperly decrease the support rigidity, in the vehicle width direction, of the suspension cross member during the normal vehicle traveling as well.